Strategic Quality Management of Aero Gas Turbine Engines, Applying Functional Resonance Analysis Method

Failure analysis and defect investigation of aero gas turbine engines, which are complex and safety-critical systems, call for advanced tools and techniques in the customer perspective framework of Strategic Quality Management (SQM). Functional Resonance Analysis Method (FRAM) is such a tool for failure mode and root cause analyses, helpful in instituting suitable corrective and preventive actions. Repeated failure of the drive shaft of oil cooling system of a turboshaft aero-engine at the Shear neck resulted in many premature withdrawals affecting fleet serviceability. Defect investigations attributed the failure initially to the Nitrided surface of the drive shaft, then the Heat treatment process, and subsequently the machining method. SEM analysis of the fracture surface showed High-Cycle Fatigue (HCF) as the failure mode. Instrumented experimentation conducted subsequently revealed a “Backward Whirl” phenomenon, initiated from the unbalance of an adjacent component and manifested at a certain range of gas generator speed, as the root cause of the HCF and consequent failures. The FRAM methodology helped in completely obviating the failures by various remedial measures, like removal of the unbalance, micro-shot peening of the shear neck, and damping of backward whirl using bearing liner bushes and enhancing stiffness by increasing the shear neck diameter to shift the backward whirl beyond the operating range of the aero-engine. The case study also demonstrates the application of FRAM for defect investigation of aero gas turbine engines.